This invention relates to a membrane filtration apparatus for effecting filtration of a liquid composition wherein a feed liquid is introduced into the apparatus and,a filtrate stream is removed from the apparatus. More particularly, this invention relates to a tangential flow membrane filtration apparatus or dead ended membrane filtration apparatus which are formed and selectively sealed by injection molding of a polymeric composition.
Prior to the present invention, liquids have been filtered within a plurality of filter modules that are stacked between manifolds or individually sealed to a manifold plate. Each module includes a one or more filter layers separated by appropriate spacer layers, such as screens, to permit liquid feed flow into the apparatus as well as filtrate flow from the apparatus. Filtration within the module can be conducted as a tangential flow process wherein incoming feed liquid is flowed tangentially over a membrane surface to form a retentate and a filtrate. Alternatively, filtration can be conducted as a dead end mode wherein all incoming feed liquid is passed through a membrane filter with retention of solids and other debris on the membrane filter. In this latter mode only a filtrate is recovered.
At the present time, filtrate is sealed from feed within a membrane filtration apparatus by sealing techniques utilizing potting adhesives, solvent bonding or heat sealing. In the case of a tangential flow filtration apparatus, filtrate is sealed from feed and retentate. Adhesives are undesirable since they have limited chemical compatibility, are a source of significant extractable species, introduce process control difficulties, impose bond strength limitations, impose use temperature limitations and increase process cycle time. Heat sealing is undesirable since its use imposes a limitation upon the thickness of the material being heat sealed. In addition, heat sealing is undesirable because it requires multiple steps, imposes material compatibility limitations and requires a substrate to effect heat sealing of filtration elements. Solvent bonding is undesirable since solvents impose environmental limitations and impose limitations on liquids to be filtered.
Accordingly, it would be desirable to provide a multilayer filtration apparatus which utilizes a plurality of filtration modules wherein the layers are appropriately sealed without the use of adhesive, solvent bonding or heat sealing. In addition, it would be desirable to provide a tangential flow or a dead ended filtration apparatus containing a plurality of filtration modules which can be formed into a stack and which can be appropriately sealed to define liquid flow paths within the stack in a one step sealing process.
In accordance with this invention, a dead ended or tangential flow filtration apparatus is provided which includes a plurality of spaced-apart membranes and a plurality of spacer layers having channels or openings that promote liquid flow therethrough. The dead ended filtration apparatus are provided with at least one feed port and at least one filtrate port. The tangential flow filtration apparatus are provided with at least one feed port, at least one filtrate port and at lease one retentate port. The membranes are included within modules each of which has at least one membrane layer and at least one spacer layer. The modules are presealed by any convenient means so that they can be subsequently sealed with additional modules and spacer layers by an insert molding process to form a membrane filtration apparatus formed from a stack of membranes and spacer layers which permits filtration of a liquid. An optional end cap can be provided at each end of the stack to assure liquid flow from the feed inlet to the retentate outlet, through a membrane, and to the at least one filtrate outlet. The spacer layers are appropriately sealed and side surfaces and end surfaces of the membrane filtration apparatus are appropriately sealed by insert molding with a molten polymeric composition which is caused to migrate into selected volumes of the spacer layers to effect sealing and to assure liquid flow within the stack, during use, from the feed inlet to the at least one filtrate outlet. In the case of a tangential flow filtration apparatus, liquid flow within the stack is assured by sealing the feed inlet and the retentate outlet from the filtrate outlet. Insert molding is accomplished by positioning the stack within an injection mold and injecting the molten polymeric composition into the mold to effect sealing in a manner that assures the desired liquid flow within the final membrane filtration apparatus during use. The spacer layers which accept filtrate are sealed by the plastic composition from a feed port extending into the stack so that the feed must pass through a membrane layer prior to entering a filtrate spacer layer. In addition, the spacer layers adjacent to the feed port which are designated to accept feed remain in liquid communication with the feed channel. Channels which accept either retentate or filtrate also extend into the stack. The channels which accept retentate are sealed from the filtrate spacer layers and are in fluid communication with the spacer layers which are also in fluid communication with the feed port. The port or ports which accept filtrate are sealed from the spacer layers which accept feed or retentate and are in fluid communication with the spacer layers that accept filtrate. The stack is also sealed in a manner so that liquid feed entering the feed spacer layers must pass through a membrane before entering a filtrate spacer layer. Prior to insert molding the stack, the stack is formed from single spacer layer units and multilayer modules which modules are partially presealed so that, in combination with the final insert molding step, the presealing assures the desired liquid flow through the final membrane filtration apparatus.